Abstract

Abstract

Plants tolerate widely varying proportions of salts in the root media but nutritional imbalances and specific ion toxicities may occur if one salt predominates under saline conditions.

The relative sensitivity of sesame (Sesamum indicum L.) to various ions and the nature of the specific ion toxicities were studied in water culture experiments. At 0.10 MPa osmotic pressure, NaNO3, NaCl, Na2SO4, and CaCl2 reduced the yield (shoot + pods) of Sesame by about 15, 26, 33, and 65%, respectively. At 0.20 MPa, Ca(NO3)2 was more injurious than NaCl or any combination of the two salts.

Chemical analyses indicated that sesame roots did not accumulate C1, Na, and Ca readily, since the accumulation factors for these ions were near or less than 1. However, leaves accumulated these ions to a considerable extent. Leaf Na concentrations of 162 µmol/g fresh wt were associated with necrosis but no evidence of C1 toxicity was noted. Calcium-induced necrosis seemed indirect, possibly a consequence of decreased Mg concentration. Ion concentration gradients indicated a specific accnmulation of Na in the stem. This retention was greater, and less Na reached the leaves, when the anion was C1 than when it was SO4, a difference that may explain the greater sensitivity of sesame to Na2SO4 than to NaCl.

The high sensitivity of sesame to single-salt salination emphasizes the importance of using salt mixtures in salt tolerance studies. At extreme Na-Ca ratios, ionic imbalance predominates and growth suppression exceeds that due to osmotic stress.

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